CONCEPT OF FRAMED STRUCTURES

Principles of Framed Structures

Framed structures are the structures which are formed by connecting a series of horizontal and vertical structural members in suitable positions. The framed structures primarily comprise of columns and beams. Columns are connected by beams at floor and roof levels. The floors are divided into rooms and passages of required sizes by walls.

The walls may be load-bearing walls or partition walls. The materials used for framed structures, in general, may be wood, steel or RCC. Light framed structures are constructed of wood, steel or RCC, whereas multi-storeyed framed structures are constructed of mild steel.

The entire load of floors, roofs and partition walls are supported by the beams which transmit these loads to the columns. These columns finally carry the whole weight of the structure to the foundation.

18.2.2 Materials Used for Framed Structures

As discussed earlier, the materials used for framed structures, viz., wood, metal and RCC, are discussed below.

1. Timber

Use of timber for framed structures offers several advantages like beauty, versatility, durability, low cost, high strength-to-weight ratio, excellent electrical insulation and high shock absorption capacity. Variety of range of finishes can be provided to satisfy decorative and protective purposes.

In wooden frames, the walls are conventionally built with slender studs spaced about 40 cm centre to centre. In a similar way, joints and rafters which are supported on the walls are also spaced 40 cm apart. Timber studs are usually placed in walls and partitions keeping the wide faces perpendicular to the face of the wall or partition. For attachment to studs, joints and rafters, facings and decking for the required sizes are available. Wood bearing wall constructions are generally either braced to balloon frame or platform frame.

2. Steel

In general, steel framework supports all loads. In this type, all columns, beams and girders in the framed structure are of steel section. Adequate bracing is needed for these structures in order to resist the wind and earthquake forces.

For these structures, fire-proof and other light materials are used for partitions and exterior walls if it is a building. Steel framed structures are capable of sustaining greater load in a given space. In steel framed structures, circular or curved work should be avoided.

3. RCC

Reinforced cement concrete (RCC) forms the best material for framed structures, provided they are properly designed and constructed. As discussed earlier, columns and beams are interconnected with each other so as to form a grid of the beams and girders. In order to carry various floor levels, the slabs are built monolithically. The foundations may be either isolated or combined footing or it may be a raft or mat depending on the soil and the load on the foundation.

Advantages of Framed Structures

Following are the advantages of framed structures:

1. If the framed structure consists of several floors, for example, in a building, it is possible to carry out different activities simultaneously. For example, finishing of lower floors can be done while the construction of framework of upper floors can be taken up.
2. Based on the requirement, the panel walls may be changed to a different position. This brings in greater freedom in planning.
3. In a building, this helps to divide the components into two distinct categories, viz., load-bearing and non-load bearing. This enables to construct the non-load bearing components using low cost materials.
4. The framed structure construction requires thin panels which in turn leads to the larger floor area. However, outer walls are off a type which shall offer heat and sound insulation and shall withstand weather conditions.
5. Framed structures can highly resist vibrations and ideal for seismic zones.
6. Very suitable in filled-up or soft ground compared to ordinary masonry constructions.

Tall buildings are generally of framed structures which are discussed in the next section.